Plant products such as tapioca, corn, rice, potato, sweet sorghum contain starch that used as feedstock for the production of ethanol. According to conventional process, starch containing agricultural products are grinded and made starch slurry or gelatinized with water for enzymatic hydrolysis. The starch slurry is cooked and liquefied by alpha amylase or liquefying enzyme at 95° C. and pH 6 for 2-3 hours. The liquefied slurry thus obtained is subjected for further hydrolysis to glucose by saccharifying enzyme, glucoamylase at lower temperature (40-60° C.) and pH 4.0 to 4.5 for 6 hrs. The glucose syrup thus obtained is then fermented using yeast, Saccharomyces cerevisiae at 30° C. and PH 4.0 to 4.5 for about 48 hrs. The fermented broth is then distilled at 75° C. to recover ethanol of 95% purity. The total time required for conversion of starch to ethanol in the fermentation broth in the conventional process is around 65 to 75 hrs.
Improvement in the efficiency of conventional process has been made by developing simultaneous saccharification and fermentation (SSF) process in which saccharifying enzyme can function under the same conditions of fermentation at 30° C. and pH 4.0 to 4.5. The process significantly saves time and energy during saccharification and fermentation process. However SSF process has the drawback on high energy input for liquefaction at 90° C. and ethanol recovery at 70° C. after fermentation at 30° C.
In the prior art such as described by Yamamoto et al. in U.S. Pat. No. 4,474,883 (1984) raw root stock starch is liquefied by bacterial amylase at 80-90° C. and pH 5.0. The resulting solution is hydrolyzed by glucoamylase and then fermented by yeast at 25 to 30° C.
In prior art Verma et al. 2000, Bioresource Technology, 72:261-266 reported bioconversion of starch to ethanol by coculturing Saccharomyces diastaticus and Saccharomyces cerevisiae in a single step process; the process was conducted at 30° C. and ethanol production decreased beyond 37° C. Therefore the process has the limitation of high input of energy for distillation of ethanol.
Bunni et al. in processing and quality of foods vol. 2, eds. Zeuthen P., Cheftel, J. C., Ericisson, C., Goemly, T. R., Linko, P., Paulus, K. pp 174-280, Elsevier Applied Pubs. Reported that the thermophilic fungus, I CBS 814.70 is capable of producing a relatively thermostable amylolytic enzymes at 45° C. on starch. Direct bioconversion of starch to ethanol using the co-culture of fungus Talaromycea emersonii CBS 814.70 and Kluyoveramyces marxiamus IMB3 at 45° C. was demonstrated by Ward et al. (Applied Microbiology and Biotechnology 43, pp 408-411) in which maximum ethanol concentration of 1.5% was reported in 40 hrs representing 70% of the theoretical yield.
Ethanol production at elevated temperature and alcohol concentration by using Kluyoveromyces marxianus IMB3 was reviewed by Singh et al. World Journal Microbiology 14, 823-834 (1998) in which they have reported mixed culture fermentation on starch containing media (4% w/v) capable of production 12 gl−1 in 65 hrs at 45° C.
In the prior art methods, handling of starch is difficult at normal fermentation temperature (45° C.) due to high viscosity and gel forming tendency of starch. Liquefaction of starch is necessary before starch is saccharified and fermented. Time required for overall conversion of starch to ethanol was longer than 40 hrs. in the most prior art for ethanol production from starch was done by using two microorganisms used in two different steps operating at different conditions. The conventional process require high input of heat and agitation energy for liquification of starch slurry at 95° C.; cooling of the slurry is required to 40 to 60° C. for saccharification by glucoamylase at pH 6.5. Further cooling is required to 30° C. for fermentation by yeast Saccharomyces cerevisiae. 
Therefore new enzymes that can simultaneously liquifying and saccharfying preferably at higher temperature e.g. above 40° C. is required so that hydrolysis can be carried out at a faster rate. Further fermentation of monosaccaharides obtained from starch hydrolysis can be carried out at faster rate by using thermophilic ethanologens.